The SRX has open proxy id by default so that any ip address can be encrypted and sent in the tunnel. This is not supported on Sonicwall. So you will have your pairs of allowed traffic setup on that tunnel via proxy id or tunnel selectors.
This means that only the local address subnets on those lists will be allowed to enter the sonicwall tunnel. So likely your remote spoke sites are not on this list.
You can ask that the sonicwall tunnel be expanded to include all the subnets that you want to include as traffic. But if you have a very large number of sites there is likely a limit to the number that can be put there.
The other option is to source nat the spoke site address to a local address on the SRX that is allowed in the sonicwall tunnel. Then the traffic can go into the tunnel and be returned.
However, this will only work for traffic that is geneated by spokes into the sonicwall tunnel. The remote sonicwall devices will not be able to initiate the session.